1. Field of the Invention
This invention relates to a combustion-powered tool, more particularly to an oscillation reducing suspension device for a fan motor of a combustion-powered tool, such as a pistol-like tool powered by a pressurized fuel gas for driving a fastener into a workpiece.
2. Description of the Related Art
Referring to FIG. 1, a fan motor suspension mechanism for a combustion-powered tool disclosed in U.S. Pat. No. 7,118,018 is shown to include a cylinder head 11 defining a cavity 111 to accommodate a fan motor 13 therein. An armature shaft 131 of the fan motor 13 extends through a floor wall of the cavity 111 to drive rotation of a fan 12 that is disposed in a combustion chamber (not shown) for providing efficient combustion within the chamber. The suspension mechanism further includes an inner annular ring 15 attached securely to a surrounding wall of the fan motor 13, an outer annular ring 16 secured to the cylinder head 11, and a central resilient web 14 extending radially between the inner and outer rings 15, 16 and configured to allow slight axial movement of the fan motor 13 so as to provide resilience to the fan motor 13 and thus shock absorption for the motor 13 upon combustion in the combustion chamber. However, due to the configuration of the central resilient web 14 that is liable to be deformed, assembly of the motor 13 is difficult to conduct and connection between the motor 13 and the cylinder head 11 is unstable. Slippage of the motor 13 from the suspension mechanism may occur during oscillation of the motor 13 in the course of operation of the tool.
Referring to FIGS. 2 and 3, another motor suspension mechanism for a combustion-powered tool is disclosed in U.S. Pat. No. 6,619,527, and includes a cylinder head 81 for accommodating a fan motor 83 such that an armature shaft of the motor 83 extends through a floor wall of the cylinder head 81 and drives a fan 82, a rigid circular motor retaining cup 84 attached to the motor 83 and providing a heat and dirt barrier for protecting the motor 83, and a mounting bracket 88 secured to the cylinder head 81 by means of fasteners 87. The mounting bracket 88 includes inner and outer sidewalls 881, 882 which are respectively attached to inner and outer portions of an annular resilient web 89 so as to secure the mounting bracket 88 to the retaining cup 84. The resilient web 89 is provided to minimize the operational dynamics of the combustion chamber caused by the combustion on the motor and also to protect the motor from axial acceleration and large oscillations. In addition, the mounting bracket 88 is retained in an axially spaced relationship relative to the cylinder head 81 by resilient spacer members 86. Thus, a shock absorbing and isolating effect to decrease the operational dynamics of the combustion chamber caused by the combustion on the motor 83 can be achieved to thereby protect the motor 83 from axial acceleration and oscillations. Since the resilient web 89 is confined by the inner and outer sidewalls 881, 882, the damping force of the resilient web 89 is reduced, and the resilient spacer members 86 are additionally required, thereby rendering the construction of the suspension mechanism complicated and assembly inconvenient.